Automatic sample changer for radioactive samples



July 15, 195,8 R. l.. MEEDER 2,843,753 AUTOMATIC SAMPLE-CHANGER FORRADIOACTIVE SAMPLES Filed Jan. 21, 1954- v s sheets-sheet 1 92 K i I i l/54 /JZ July 15, 1958 v R. L. MEEDl-:R l 2,843,753 AUTOMATIC SAMPLECHANGER FOR RADIoAcTIvE SAMPLES Filed Jan. 21, 1954 v e sheets-sheet 2July 15,1958 R. L. MEED'ER v 2,843,753

AUTOMATIC SAMPLE CHANGER `FOR RADIOACTIVE SAMPLEIS Filed Jan. 21, 1954 fe sheets-sheet s July 15, 1958 R. L. MEEDER 2,843,753

AUTOMATIC SAMPLE'CHANGER FOR RADIOACTLVE SAMPLES Filed Jan. 2l,v 1954 6Sheets-Sheet 4 y July 15, 1958 R. l.. MEEDER 2,843,753

v AUTOMATIC SAMPLE CHANGER FOR RADIOCTIVE SAMPLES e sheets-sheet f 5Filed Jan. 21,v 1954 QNN m EL NNN mm@ NNN IUFSm.. R

v July 15, 1958 R. L. MEEDl-:R

' AUTOMATIC sAMPLEcHANGER FOR RAnroAc'rIvE SAMPLES Fileq'Jan. 21. 1954WNN 6 t w m w 6 l .Iam mnhummm mmmmm A@ j @N 55 @we m amwmzmu mz ,rz:5zu www@ o DE e o um ,wumm e @md5 mzn um 5 o NNN NNN \N E mzL Jef? for.'@wlorld /yee del AUTOMATIC SAMPLE CHANGER FOR RADIOACTIVE SAlVlPLESRaymond L. Meeder, Palos Heights, lll., assignor to Nuclear-ChicagoCorporation, a corporation of Illinois yApplication January 21, 1954,Serial No. 405,309

n 21 Claims. (Cl."250 106) This invention relates to devices for themeasurement of the radioactivity of radioactive materials, and morespecifically to an automatic sample ychanger for making successlvemeasurements of the radioactivity of a large number of samples.

It is common, in laboratories and other installations wherein work isdone with radioactive materials, as, for example, inbiological, medical,radiochemical, and similar laboratories, to make successive measurementson large numbers of `radioactive samples or specimens. Up until arelatively'short time ago, it was universal practice for the techniciansor scientific or medical personnel performing these measurements tomanually place each radioactive sample or specimen to be counted in alocation suitably adjacent to the radiation detection device beingemployed, and then to manually remove each sample upon termination ofthe desired counting interval, the interval being determined bythe'reaching of a predetermined count or the expiration `of -apredetermined time. More recently there have been designed automaticsample changers, in which there are inserted'a large number of samples,suitable mechanism being provided to successivelyk expose the samples tothe radiation detector employed, such automatic sample changers havingfacilities for connection to suitable counting, timing and recordingapparatus, so that each sample is automatically exposed to the radiationcounter for a predetermined time (in which case the number ,of countsobtained from each sample during the constant interval is recorded onkthe recording apparatus), or until a predetermined count is obtainedfrom each sample (in which case the quantity recorded is the amount oftime required for each sample to give the predetermined count).

The automatic sample changers heretofore designed and made available aresubject to a number of objections which have greatly limited the use ofsuch automatic sample changers. For one thing, the automatic samplechangers heretofore devised have been extremely complex from themechanical standpoint, thus making the cost of `constructing such asample changer and of maintaining` the mechanism extremely high.Additionally, the auto.- matic sample changers heretofore devised havebeen extremely bulky, requiring large areas of desk or table space.

Further, the relatively numerous and complex manual operations involvedin loading and unloading batches of samples into and from the priorsample changers have been sufficiently time-consuming to considerablyreduce the time-saving advantages to be obtained in employing anautomatic sample changer instead of using ordinary manual manipulationof samples.

The present invention provides an automatic sample changer forradioactive samples which is not subject to these objections.

The automatic sample changer of the present invention is both simple andcompact. The manual operations required, both in loading and unloadingthe changer, and in obtaining the radioactivity data,

fare minimized. The constructional simplicity substan- '2,843,753Patented July 15, 1958 ICC Figure 3 is a transverse-sectional View of asample l holder or adapter designed for use with the sample changer; v nFigure 4 is a horizontal sectional view taken along the line 4 4 yofFigure 1 in the direction indicated by arrows;

Figure 5 is a similar sectional view taken along the line 5 5 of Figure1 in the direction indicated by arrows;

Figure 6 is a horizontal sectional view' taken along the line 6 6 ofFigure 1 in the direction indicated by `aITOWS;

Figure 7 is a fragmentary vertical sectional view taken along the line 77 lof Figure 2 in the direction indicated by arrows;

Figure 8 is a schematic electrical diagram of a control circuitconstituting the electrical portion of the samplel changer, andillustrating the interrelation between theV electrical and mechanicalcomponents thereof;

Figures 9 and 11 are fragmentary detail views; and

Figure l0 illustrates the control panel of the device.

In describing the embodiment of thevinvention illus-V trated,understanding yof the invention and of its essential. teachings will befacilitated by vseparating the descriptions ofthe component assembliesvwhich form the device by appropriate headings. Thus there will rst bede-. scribed the stationary assembly comprisinga'radiation shield, firstand second magazines each adapted to receive aplurality of sampleholders, andmeans for 'supporting bly, vand also to synchronize andinterlock the operation of the sample changer with timing, counting, andrecording equipment to which the sample changer mayv be connected.

The stationary assembly f The vlower housing 12, which supportsthedevice on a table or bench upon which it is placed, isalgenerallyrectangular open-bottom base provided with a sloping front panel 14appropriately aperturedto permit the mounting thereon Lof the electricalcontrols and indicators generally j designated by the numeral 16,. andlater kto kbe described in connection with the electrical system. Anopening or cut-out 18 in the rear surface of the bottom housing 12permits access for making electrical connections to an aluminum chassis2t) of L-shaped cross section which isk mounted within the lower housingl2. (It willbe understood that the relays and other electrical circuitcomponents later to be described, but illustratedvonly in the electricalschematic diagram of Figure 8, are mounted on the l chassis 20 inaconventional manner, being omitted from the mechanical portion of thedrawing for purposes `of clarity.) Rubber feet 22 are secured byscrews24 to internal ribs 26 cast integrally with the lower housing 12.

Resting on top of the lower housing 12 on 'a ridge 28 formed thereon isan upper housing30, secured to the lower housing 12 by bolts 32. Theupper housing 30 consists generally of a substantiall, oval rim 34, thelower edge of which rests on the ridge. 28, and a network `ofinterconnected ribs or webs 36, 3S, 40.42, 44, and 46, which are formedintegrally with, and constitute the support for, apertured bosses 48,50, 52'and5'4. These bosses are so spaced thatthe apertured. boss 50liesat 'the center of a circle upon the circumference of whichl liethebosses 48, 52, and 54, disposed at 120 degree intervals. Forcefittedinto each of the bosses 4S, 52 and 54 is an oil-impregnated sleevebearing 56, and a similar bearing 58 is provided in the aperture of boss50. An additional rib or web 60 extends along an arc of .theaforementioned circle, connecting the bosses 52 and ,54, and a dat plate62 of similar curved shape is bolted to the arc-shaped rib or web 60 bybolts 64. The plate 62 is preferably of a bearing material such asoil-impregnated bronze and is notched at its ends to conform to thecircular shape of the apertures in the brosses.

Resting atop the upper edge of the upper housing 30 is a thick mountingplate 66 of the same general outline as the upper` housing 30. Themounting plate 66 is bolted at 68 to support ribs or lugs 70, 71, and72, which are cast integrally with the upperpart of the upper housing30, and extend inwardly from the rim 34 flush with the upper edgethereof. Theribs of lugs 70, 71 and 72 are all on the rearward portionof the upper housing 30. The front portion of the upper edge of thehousing 30 is cut away, the upper edge being offset at 74 to permitpassage of a carriage, later to be described, between the front portionof the upper edge of the housing 3,0 and the mounting plate 66. Thus themounting plate 66 is rested upon, and secured to," the upper housing 30only in the rearward portion thereof, the forward portion of themounting plate 66 being cantilevered.

In the rearward portion of the mounting plate 66 is a largebore76"having its center above the rearward boss 48 in the upper housing30, and having an upwardly facing rabbet or shoulder 78. Seated on theshoulder 78 is the lower edge or mouth portion of an open-endedradiation shield 80. The shield 80 consists in general of a thick sleeve82 of lead encased in a steel jacket 84. To the upper end of .thecylindrical shield is afxed a mounting ring 86 by means of which thereis mounted thereon a radiation detection assembly including a housing8,8 snugly fitting into the aperture in the shield. A socket 90 isprovided in the bottom `of the housing 88 and a cable 92 is connectedthrough the housing 88 (which may contain a preamplifier) to the socket90. In the drawing there is illustrated a radiation detector 94, whichmay be, for example, a Geiger-Muller tube or a scintillation counter,provided with a suitable plug inserted in the socket 90. The shield anddetector assembly are not illustrated in further detail in the drawing,since they in themselves constitute no part of the present invention.

In the forward portion of the mounting plate 66, centered above thebosses 52 and 54, are bores or apertures 96. The circular bores 96 areso located in the mounting plate 66 that they are at the edge of theplate 66 and thus form interruptions in that edge. The neck openingswhich are thus formed between the bores 96 and the outer edge of themounting plate 66 are flattened ol` at 98 to permit the attachment ofclips hereinafter to be described. Seated in the bores 96 are the lowerends or mouth portions of long tubes of transparent plastic which areemployed as loading and unloading magazines, as will be more completelyset forth hereinafter. The tubes or magazines 102 and 104 have thecircumferential portion thereof corresponding to the opening between theflattened surfaces 98 of the neck entries to the bores 96 cut away toform slots for access to the interior. Spring clips 106, screwed to theneck portion 98, secure the tubular magazines 102 and 10,4 againstrotation in the.

l bores 96. Security of positioning of the magazines '102 and 104 isfurther assured by screws 108 securing the magazines to the mountingplate 66, and by rabbeting of the lower ends of the magazines.. A

In Figure 3 is shown a cross sectional view of a sample holder oradapter 110, which is designed yfor use in the device. The adapter,which lis preferably made of alu"- minum, is essentially a disc or waferhaving centrally thereof a plurality of shoulders 112 and 114 ofdiminishing diameter. These shoulders 112 and 114 'are designed toreceive and support sample .pans of the type conventionally used inspecimen counting. The bottom of the holder 110 is apertured at 116 topermit ready removal of a sample pan from the holder or adapter 110. Theprovision of shoulders of different diameters permits use of the holders110 with a plurality of sample pan sizes, and a substantially largernumber of shoulder diameters may be provided if desired. The edges ofthe holders 110 are rounded at 118 to facilitate insertion of a `holderat the bottom of a stack of similar holders, as hereinafter to bedescribed. .Ridges 120 are formed in the top of the holder in order tominimize friction as a holder is slid into or from the bottom of astack, While at the same time preventing jamming which may occur if onlya single lip or ridge is employed. The holders 110 are of a diameter toslide freely, but without excessive `play,rir1 the tubes or magazines102 and 104.

As will more fully appear below, the magazine 102 is employed as areceiving magazine, and the magazine 104 as a dispensing magazine. Inoperating the device, the samples to be counted are inserted in holders110. The holders 110 are then stacked in the dispensing magazine 104.Whenthe device is then placed in operation, successive-samples are movedbeneath the shield 80, inserted into the shield so that the detector 94measures the radioactivity, lowered out of the shield, and moved to thebottom of the magazine 102, wherein they are received in the reverse oftheir original order. The structure of the magazines 102 and 104 notonly simplifies the operations of loading and unloading the device, butalso permits ready access to the samples for such purposes as makingsubstitutions or changes in order. The means for with drawing thesuccessive sample holders from the dispensing magazine and insertingthem into the shield and for withdrawing them from the shield andinserting them into the recervmg magazine will be described below.

T he carriage assembly .Beneath the mounting plate 66, which supportsthe magazines 102 and 104 and the shield 80 as described above, 1s acircular carriage plate 122, which is rotatably mounted with its centerdirectly above the boss (the manner of mounting to be more fullydescribed hereinn after) and has circular recesses in its upper surfaceat 124,

126 and 12S, These circular recesses are equally spaced and are ofessentially the same diameter as the bottom openings in the shield andthe magazines 102 and 104, 1. e., of a diameter to receive freely sampleholders 110. rlhe circular recesses intersect the periphery of thecarrlage 122 and thus form interruptions in the upper portion of theedge of the carriage. Reciprocable in the respective recesses 124, 126and 128, and normally resting on the bottom thereof, are elevating discs130, 132, and 134, of essentially the same diameter as the sampleholders. The thickness of the discs 130, 132 and 134 is so related tothe depth of the recesses 124, 126 and 128 that when the disc is restingon the bottom of the respective recess, the upper surface of the sampleholder within the recess lies substantially flush with the surface ofthe carriage. In this manner a sample holder 110 within one of therecesses may be slid under or out from a stack ol similar holders in thereceiving magazine 102 or dispensing magazine 104 by rotation of thecarriage 122. The upper surface of the carriage 102 is provided withconcentric ribs or ridges 136 upon which stacks of sample holders withinthe magazines ride or oatas the carriage is rotated from one position inwhich'there is arecess beneath each of the magazines and the shield andthe next such rotational position. Depending from the centers 'of therespective discs 130, 132 and 134, through guide face of the carriage,and the carriage is then again moved,

the sample holder which was previously in the recess will remain in themagazine and become the bottom-most sample holder in that magazine.

The drve'assembly Extending through the respective sleeve bearings 56 inthe bosses 48, 52, and 54 are tappet or lifter pins 144, 146 and 148having heads of suicient size to prevent their falling through thebearings. The pin 144 which is beneath the aperture in the shield 80 issubstantially longer than the pins 146 and 148,v which are beneath thereceiving and dispensing magazines.

Mounted on the chassis 20 is a motor 150 having an upwardly extendingshaft 152. The shaft 152 is coupled by a bayonet connection 154 to aspindle 156, which is externally threaded at 158, a cam wheel 160 beingthreaded on the spindle 156 and locked in position by a locknut 161. Thespindle is formed with a flange 162 which rests on the end of sleevebearing 58. Fitted over the upper end of the spindle 156 and supportedby the flange 162 is an apertured friction plate 164. Around the upperend of the spindle 156 is a tubular bearing 166.

The carriage plate 122 has a central aperture fitted over the tubularbearing 166, the under surface of the carriage plate 122 thus resting onthe upper surface of the friction plate 164. The upper surface of thecarriage plate 122 is centrally recessed at 168. Within this recess isa'spring 170 which is compressed between the bottom 4of the recess 168and a retaining washer 172 by a screw 173 which is threaded into theupper end of the spindle 156.

It will be seen that the pressure exerted by the spring 170 creates africtional engagement between the carriage 122 and the friction plate164 and also between the friction plate 164 and the flange 162k on thespindle 156. The restoring force of the spring 170 is so chosen that thecarriage 122, when loaded with sample holders in its recesses, is easilyrotated by rotation of the spindle 156. However, when, as appears below,the carriage is locked in position, the spindle 156 may continue torotate without undue wear on the par-ts. Thus it may be seen that thecarriage 122 will normally be driven by the spindle 156, which isrigidly coupled to the motor 150, but the locking of the carriage in anygiven position, as by a fixed stop, permits the spindle, and the cam160, to continue to rotate during the running of the motor 150.

The cam 160 is essentially a wheel having on the circumference thereof acamming lobe or rim 174 extending through an arc of approximately 120degrees. The cam lobe is of maximum thickness or height at the centerthereof, where it is essentially flat on top over an arc ofapproximately 20 degrees, as shown at 176. On either side of the highestportion 176, the rim or lobe 174 Vis tapered -downwardly through a 50degree arc. surface which raises and drops the tappet or lifter pins144, 146 and 148 in the manner hereinafter described. Additionally, onthe outer or peripheral surface of the It is thisA .Y

lobe 174 there are provided radial tapers 178 at each end of the lobe,and a central radial projection 179 which is flat in a small centralregion ofthel periphery, as indicated at 180, tapering radially to theradius of the bulk of the lobe 174, as shown at 182Within thewZOwr 6degree arc of the'vertically dat portion 176. The bottoni of the radialprojection 179 is cut away at 181. The purpose and operation of theradial camming surfaces on the cam wheel 160 will be described below inconnection with the electrical system. l

The aggregate slope or pitch of the cam lobe 174 between the flatcentral portion 176 andthe tapered ends is such that when the centralelevated lportion 176 supports either of -the lifter pins 146 or 148,the lifter pin is elevated to an extent suflicient to raise the tappetpin 138, or 142 which is thereabovev to the level lwhere the uppersurface of the disc 130, 132 or'134 is substantially flush with theupper surface of the carriage. The lifter pin 144 is, as stated above,substantially longer than the lifter pins 146 and 148. Thus when therotational position of the yearn 160 is such that the elevated portion176 supports the pin 144, the disc 130, 132 or 134 which is then abovethe cam surface 176 is elevated substantially above the surface of thecarriage into` the shield 80.

The manner of cooperation of the drive assembly vwith the carriageassembly 1o produce the manipulation of the samples described above inconnection with the stationary assembly will now be readily understood.Each sample-changing operation is commenced in the cam position whereinthe at portion 176 at the apex of the cam lobe 174 supports the lifterpin 144, so that a sample 110 is supported well within the radiationshield 80. Ity will be understood that since the entire construction of`the carriage 122 is symmetrical about its axis ofl rotation, therecesses 124, 126, and 128 and their associated moving parts beingidentical, the manner'of operation. is the same irrespective of which ofthe recesses is posi-V tioned beneaththe shield 80 at the commencementof operation. However, for ease of explanation, the suc' ceedingdescription of a change cycle will be based on the startingposition asshown in the drawings, i. e., with the recess 124 beneath the shield 80.

The motor drives the -spindle 156 in a counterclockwise direction (asviewed from the top). As the. cam commences to rotate with the spindle156, thecarriage 122 remains stationary due to the fact that the lowerend ofthe tappet pin 142 is positioned againstV the end of the plate 62,which thus serves as a stop member in the portion of the rotational pathof the depending tappet pins adjacent to the receiving magazine, 102,locking the carriage 122 against rotation. Thus as the cam 160 commencesto rotate, the only motion in the carriage plate assembly is thelowering of the sample 110 from the shield 80 to the point where theupper tially ush with the upper surface of the carriage 122. Thus thesample holder within the recess 128 (remaining there from the previouschange operation) is elevated into the receiving magazine 102, atthetbottom of thev stack deposited there by previous sample-changingoperations. At the same time the lower end of the tappet pin 142 iselevated suiciently to be disengaged from the end of the plate 62, sothat the carriage plate122 is unlocked. Thus for the next one third of arevolution of the cam 160, the carriage plate 122 rotates with the cam,the recess 124 thus `being brought around to the point beneath thereceiving magazine 102. At the same time the sample holder which was atthe bottom of the stack in dispensing magazine 104 in the recess 126slides out from beneath that stack and is placed beneath the opening inthe shield 80. Meanwhile, the bottom end of the tappet 142 is'supportedon the top surface of the plate k,62, so that the, sample VholdernwhichVwas Y,

previously supported on the disc 134 is left behind in the receivingmagazine 102, supported in floating fashion by the ribs 136 on thecarriage 122. During this one-third of a revolution of the cam 160, thelifter pin 148 is lowered to its normal position, and the lifter pin 146is elevated. The continued elevation of the disc 134 permits it to slidein at the bottom of the stack of sample holders in the dispensingmagazine 104. At this point the carriage 122 is again locked in positionbecause the next tappet pin 138 is now engaged by the end of the plate62. As the final one-third of a'revolution of the cam 160 commences, thecarriage 122 remains stationary, the disc 134 is lowered into the recess128, and the sample holder previously at the bottom of the stack in thedispensing magazine 104 is thus positioned in the recess 128. Thereuponthe new sample holder' which was removed from the bottom of the stack inthe dispensing magazine 104 by the motion of the carriage 122 during thesecond one-third of a revolution of the cam 160 is finally elevated bythe cam lobe 174 into the shield 80, to have its radioactivity measuredby the detector 94. By the means hereinafter to be described inconnection with the electrical system, the motor 150 is inactivated atthis point, and remains inactivated until the counting operation iscompleted, at which time the next change operation occurs in anidentical manner.

It will be observed that with the structure described, the cyclicalmanipulation of the samples is completely reversible by merely reversingthe direction of rotation of the spindle 156. As will be shown inconnection with the electrical system, this fact is utilized toautomatically restack all of the sample holders in the dispensingmagazine 104 after the counting of the last sample in a batch and tothen again restore the original cycle, so that the same group of samplesmay be recounted any desired number of times without the necessity ofmanipulation by an operator. lt will also be seen that the insertion ofthe sample-holder into the shield in the manner described permitsbringing the sample closely adjacent to the detector without increasingthe exposure of the detector to external radiations through the openingin the shield through which the sample is inserted.

T he electrical system Mounted on a boss 184 on the upper surface of thelower housing 12 is a snap-action switch 186 having extending therefroma lever 188 adapted to actuate the switch when struck by the radialprojection portion 179 of the cam lobe 174. The switch 186 is sopositioned as to be actuated when the cam wheel 160 is in the positionwherein the lifter pin 144 is resting on the upper cam surface 176. Asimilar switch 190 is mounted on a boss 192 one-sixth of a revolutioncounter-clockwise from the switch 186. The boss 192 is lower than theboss 184 so that as the cam rotates, the radial projection 179 clearsthe lever 194 because of the cutaway of the radial projection 179 at181. Thus the arrangement of the switches 186 and 190 is such that theswitch 186l is actuated only by the radial projection at 179, while theswitch 190 is actuated during essentially the entire first one-third ofa revolution of the cam 160 from its original position as describedabove.

A crescent-shaped plate 196 is secured to the upper surface of the innerends of the ribs or lugs 70, 71 and 72, by screws 19S, and snap actionswitches 200 and 202 are secured to the underside of the plate 196, withlevers 204 and 206 having roller ends normally resting on the upperportion of the periphery of the carriage plate 122. The switches 200 and202 are positioned somewhat clockwise and counter-clockwise,respectively, of the aperture in the shield Si), and are adjusted inposition by means of slots 208 in the plate 196' so as to sense theabsence of a sample holder from a recess 124, 126 or 128 proceedingtherepast. The levers 204 and 206 ride, as stated above, at the upperportion of the edge of the carriage `plate 122. When sample holders arepresent in the recesses in the carriage plate, the switching positionsof the switches 200 and 202 are not affected as the carriage rotates.However, if and when an empty recess appears opposite one of the levers204 or 206, the respective switch 200 or 202 is actuated as shown inFigure 9.

Referring now to the schematic electrical diagram of Figure 8, it willbe seen that the electrical system is adapted to be connected to aconventional single-phase power outlet by a power plug 210, the twosides of the power line being indicated in the drawing by shaded andunshaded triangles, and being hereinafter referred to for convenience asthe black and white side of the power line, and being provided with apower switch 209 and pilot light 211. The system utilizes a series ofrelays 212, 214 and 216, of which the actuating windings bear the samereference character with the latter w, and the contacts bear the samenumber with the letters a, b, etc. In Figure 8, the contacts are shownin their normal positions (winding circuits open), and with the contactsof each relay in vertical alignment with the schematically indicatedcore thereof.

One terminal of the motor is permanently connected to the black side ofthe line and the other terminal of the motor is connected to the whiteside of the line through a normally open set of contacts 2120 of therelay 212. The winding 214W of the relay 214 is connected between theblack side of the line and the white terminal of the motor 150. Thewhite terminal of the motor is also connected to the white side of theline through the normally open stationary contact of a double-throw setof contacts 216b of the relay 216. In

n the normal or unenergized position of the contacts 21617,

the white side of the motor 150 is connected to the normally closedstationary contact 186e of the switch 136, which is mounted as describedabove. Normally open contacts 216e: of the relay 216 interconnectterminals or binding posts designated in the drawing Print Elapsed Time,the functionof which will hereinafter be pointed out.

The motor 150 is provided with control leads 218 in conventionalreversible motor fashion, so that the connection of the common leaddetermines the direction of operation of the motor. The leads 218 areconnected to the contacts 212b of the relay 212 in such a manner thatthe motor direction is forward (counter-clockwise in the drawings) whenthe winding 212W is unenergized, and reverse when the relay 212 isactuated. One side of the winding 212W is connected to the black side ofthe line and the other terminal of the winding 212W is connected to anormally open set of contacts 212e of the relay 212 which serve, whenclosed, to connect the white side of the winding 212W to the white sideof the line through the normally open contacts of the switch 202(illustrated as in the closed position in the drawing, the normalposition of the switch 202 itself being the position assumed when itsenses an empty recess, as described above). The relay 214 is providedwith a normally closed set of contacts 214a, interconnecting bindingposts for external connection designated Timer. An additional set ofcontacts 216'b of the relay 216 normally connects a binding post ScalerGround to a binding post Scaler Reset, actuation of the relay 214connecting, in make-before-break fashion, a Stop-Count binding post tothe Scaler Ground binding post. The winding 216W has one side connectedto the black side of the power line and the other side to the white sideof the power line through a normally open manual push switch 217, andalso to the movable tap 21911 of a manual tap switch 219, to be laterdescribed.

It will readily be understood by those skilled in the art that thebinding posts described are designed to be connected to commerciallyavailable printing timers and Ito the black side of the line.

. Count terminal, andthe sealer is reset when the former terminal isconnected to the Scaler Reset terminal. As stated above, these auxiliarydevices are commercially available and do not in `themselves constituteany part of the present invention, and are accordingly not illustratedin the drawing.

The movable contact 186b of the switch 186 is directly connected to themovable tap 22011. of a three-position manually operated tap switch 220,which is ganged with a similar switch 222. The tap 2201 is alsoconnected tov one of a pairl of binding posts designated Timer Power,the other of which binding posts is connected These posts are designedto supply and interrupt the power to the timer described above, and notillustrated. Two of the stationary contacts 220a and 220e of the switch220 are connected to the white side of the power line. The thirdstationary contact 220613 is connected to the normally lopen stationarycontact 200a of the switch 200, the movable contact 20Gb thereof beingconnected to the white side of the line. The normally closed stationarycontact 200e of the switch 200 is connected to the movable tap 222]; ofthe switch 222. The stationary contact 222:1 of the switch 222, which iscontacted in the same position of the ganged switches as the stationarycontact 221m of the switch 220 (this position being designated Recyclein the drawing), isconnected to the white side of the winding 212W. Thestationary contacts 222e and 222d, which are connected to the movabletap 222b in the positions of the ganged switchesdesignated Normal andOne Cycle are connected to the black side of the line through a neonglow lamp 224 and resistor 226. The normally open stationary contact18611 of the switch 186 is connected to the black side-of the4 powerline through a.- glow lamp 228 and resistor 230. The switch 19.0 has themovable contact 1 90bl connected to the black side of the power line.

yThe cycling or timing stimulus for operation `of theV y' device isshown schematically in the upper left hand portion ofthe illustration ofFigure 8.y There is therein shown in block form ay stepping switch drive232, together with a stepping switch 234 which is driven by the drive232 as indicated by thedotted line 236. The drive 232 .and switch 234constitute a commercially available unit of the type manufactured by anumber of manufacturers of telephone relays, the drive 232 operating inresponse to pulses at the'input 238 to advance the movable contact 234beach time an input pulse is received. It will be understood that thestationary contacts 234:1 through 234k shown in the drawing constituteonly a small portion of the stationary .contacts present in such astepping switch, the unused stepping switch contacts not beingillustrated in order to simplify the drawing. In a specific constructionwhich has been employed, the movable contact or rotor 234b, which homesor zeroes at the contact 234a, progresses to contact 234cafter tiveinput pulses, 23411 after ten input pulses, 234e after twenty inputpulses, 234]c after forty input pulses, 234g after eighty inputpulses,.and 234k after one hundred input pulses. The stationary`contacts 234C through 234k are connected with respectivelycorresponding stationary contacts of the manual tap switch 219. Themovable contact 234b of the stepping switch is connected to the whiteside of the power line. It will thus be seen that upon the occurrence ofa number of input pulses to the stepping switch drive which isdetermined by the setting of the manual switch 219, the tap 219b will beconnected to the white side of the power line through the switch 234.

Additional stationary contacts 219a and 219C are provided -on the switch219. These klatter contacts are each connected to one member of a pairof binding posts 240 and 242, the opposite members of the pairs beingconnected directly to the white side of the power line. Thus it will beseen that provision is made for inserting alternative timing or cyclingstimuli in place of the stepping switch 234. For example, an ordinaryrepeating interval timer switch may be connected to the bindingy post3240, and a switch controlled by a predetermined count sealer may beconnected to the binding post 242, as hereinafter set forth. p

The power Vfor the stepping switch drive 232 is supplied from powerleads 244, `one of which is connected to the normally closed stationarycontact a of the switch 190, and the other of which is connected to thecontact 20th:, hereinbefore described. The homing or zeroing connection246 which resets-the stepping switch 234 (a facility provided incommercially available stepping switches) is connected to the normallyopen stationary contact 19de of the switch 190, and also to a bindingpost designated Timer Reset.

Overall operation The components and connections ofthe electrical systemhaving thus been described, the manner of operation thereof, and themanner of cooperation with the mechanical system previously described toform a uni-` tary automatic sample changer, will readily be understood.Since the' exact mode of operation may be varied to a considerableextent at the discretion of the operator, by setting of the controls onthe front panel of the device, as illustrated in Figure 10, it isconvenient for purposes of clarity to rst describe the completeoperation in connection with one setting of-the controls, and thereafterto describe the variants which the operator may change by making othersettings :of the controls. In Figure 10, the various switch levers andindicator lights are designated by reference characters corresponding tothose of the schematic circuitA diagram of Figure 8. The mode ofoperation will first be described with the switches 220 and 222 in theRecycle position and the switch 219 set'k to one of the numerical countpositions corresponding to.

a number of advancements of the stepping switch 234. The operator iirstloads any desired number of sample holders 110, containing samples to becounted, into the dispensing magazine 104. In the illustrated embodimentup to 50 samples may be so loaded into the device in one batch.Thereupon the automatic operation is instituted by pressing of the Startswitch 217. The closing ofthe switch 217 actuates thenrelay 216. Theresultant closingof the contacts 21611 will cause the printing timerlattached to the binding posts .Print Elapsed Time to print the elapsedtime, which will in this case be zero. The motor is actuated in theforward (counter-clockwise) direction by the closing of the connectionat 216b to the white side of the power line. The push switch 217 needonly be held down until the cam projection 179 progresses through Athesmall angle required to permit the switch 186 to return to its normalposition, at whichpoint the deenergizing of the relay winding 216W doesnot stop the motor 150, because the normally open stationary contact4ofthe contact set' 21617 is now itself connected toY tivatedordeclutchedby the action of the contacts 214a,

At the same time the sealer, whose output -pulses are coupled to theinput 23S of the stepping switch dr1ve 232, is inactivated by connectionof the Stop-Count binding post to the Scaler Ground binding post byoperation of the contacts 21419, thus effectively inactivating thedetector 94. At the end of the first l of a revolution of the cam, theswitch 19h returns to its normal position, supplying power to thestepping switch drive 232. However, for the balance of the revolution ofthe cam, the stepping switch drive 232 is not activated, because theinput 233 is inactivated by the continued connection of the Stop-Countpost which inactivates the scaler connected to the input. During thisfirst revolution of the cam, the rst sample is introduced into theshield in the manner described above. Then the cam projection 179 againactuates the switch 18o, the motor 150 is stopped, and the relay 214 isinactivated, thus starting the timer. At the same time the scaler isreset by the operation of the contacts 2Mb and activated for a countingoperation.

The mechanical assembly remains in this condition until a predeterminednumber of counts is registered by the detector 94 within the shield 80.This predetermined number of counts will be equal to the product of thescaling factor of the sealer employed with the illustrated equipment andthe preset number of pulses received by the stepping switch drive asdetermined by the position of the tap switch 219. Thus, with a scalerhaving a scaling factor of 64, and a setting of 20 on the switch 219.the system will operate in this condition until 1280 counts have beenreceived by the scaler. Thereupon the relay 216 will be energized by theresultant connection of the tap 219b to the white side of the power linethrough the switch 234. At this point the printing timer (notillustrated) will be actuated to print the elapsed time by the contacts216a and the motor will again start. At this point the stepping switchand the timer are again reset to zero by the action of the switch 190.The rst sample is removed from the shield in the manner described aboveand stored in the receiving magazine, and the succeeding sample isremoved from the dispensing magazine and inserted in the shield. Thiscycle continues until all of the samples originally placed in thedispensing magazine are measured, the printing timer thus producing arecord of the time required to reach the predetermined count for eachsample.

After the counting of the last (top) sample of the stack originallyplaced in the dispensing magazine is completed, the same operationstarts, but is interrupted when the switch 260 senses that there is nosample holder in the recess which is about to proceed to the pointbeneath the shield. At this point, the switch 200 returns to its normal(unactuated) position, disconnecting the power from the stepping switchdrive 232 and energizing the winding 212W of the relay 212. The relaycontacts 212:1 then continuously energize the motor 150 and the relay214, and the contacts 212k reverse the direction of operation of themotor 150.

As the carriage 122 commences to rotate in the reverse direction(clockwise in the drawing), the switch 200 is again actuated to open theconnection of the xed contact 200C and the movable contact 200b.However, this does not inactivate the relay winding 212W because anormally open contact 212e of the relay 212 acts as a holding Contact aslong as the switch 202 is closed. The motor 150 thus continues to rotatein the reverse direction. It will be noted that the continued operationof the motor 15@ is not interrupted by the opening and closing of theswitch 186 in this portion of the operation because the motor iscontinuously activated by the relay contacts 212e. Likewise, the relay214 is continuously activated to inactivate the timer and the sealer. Asseen above, the reverse rotation of the motor 150 acts to restore thesample holders to the dispensing magazine in their original order andthis restacking operation is independent of the actuating stimulus'whichdetermines the time that a sample holder remains in the shield duringthe forward operation (in this case the predetermined count stimulusdescribed above).

The reloading of the sample holders into the dispensing magazinecontinues until the last sample holder has been removed from thereceiving magazine. As the next recess in the carriage plate progressespast the switch 202, the latter senses the absence of a sample holder,and opens the connection of the winding 212W, thus returning thecontacts of the relay 212 to their normal position. At this point themotor again reverses to assume its original forward direction, and allof the samples are counted a second time in the same manner as describedabove. In this manner the apparatus will continue to count'theradioactivity of the batch of samples repeatedly until it is shut o bythe operator. As is well known, the continued recounting of the samplesis desirable in many cases, particularly where measurements are beingmade for the purpose of making radioactive decay curves on a largenumber of samples.

The above description of the overall operation assumes the position ofthe controls wherein the ganged switches 220 and 222 are in the Recycleposition, and the selector switch 219 is set so that each sample holder(during the forward portion of the cycle) is maintained in the radiationshield until a predetermined count is reached. In the Normal positionofj the ganged switches, the counting of the samples after the loadingthereof into the dispensing magazine occurs in the same manner as abovedescribed. However, in this position of the controls, the switch 200does not operate to reverse the direction of the motor. Now the sensingby the switch Ztl@ of an empty recess merely serves to flash theindicator light 224, which bears 0n the panel the legend CycleCompleted. The rest of the apparatus continues to operate in the samemanner as previously, the motor 150 continuing to operate in the forwarddirection, moving a new (but empty) recess beneath the shield each timethe predetermined count is reached. However, the predetermined countwhich now constitutes the timing stimulus for determining the durationof each counting and resetting cycle is the background count whichpenetrates the radiation shield (or has been deposited therein bycontamination). There is thus produced not only a record of the samplescounted, but also a record ot the intensity of the background, whichcontinues until the operator intervenes. It is to be noted that if it isso desired, the background count may also be recorded by merely omittinga radioactive sample from one or more of the sample holders, thusproducing a background count recording during the counting of the stackof samples in any position of the controls.

In the One Cycle position of the ganged switches, the operation issimilar to that in the Normal position, except that when the switch 200senses the absence of a sample from a recess in the carriage plate afterthe last sample has been counted, the motor is inactivated, since inthis position of the ganged switches the connection of the motor 150 tothe white side of the line is through the switch 200. Thus in the OneCycle position, the entire mechanism stops after the last sample hasbeen counted, and the Cycle Completed lamp 224 is illuminated.

The effect of the position of the switch 219, designated the CountSelector, will be readily apparent. ln the rst six positions of theswitch, the timing stimulus is pro` vided by the predetermined countmechanism including the stepping switch above described. When the rotor219]) is set to contact the stationary contact 219@ (the positiondesignated Time in Figure l0), the timing cycle which determines theintervals at which samples are changed is fixed by a repeating intervaltimer connected to the binding posts 240. In this case, of course, thede- 13 vice is used with a printing register .which records the numberof counts received during each timing intervals, rather than thetimeconsumed to reach a predetermined count, jas inthe previous type ofoperation.

The binding posts 242 are connected in the same manner as the bindingposts 240, theposition of the switch 219 in which the former 'bindingposts are used being designated Auto on the panel of Figure 10. Thisconnection and switch position are designed for the use of an automaticsealer, i. e., a sealer itself. containing a predetermined countmechanism, thus rendering unnecessary the employment of the steppingswitch 234 and its associated drive 232 for predetermined countoperation.

VThere is herein describedmerely a singleembodiment of the invention.Upon examination of the drawing and description above, persons skilledin the artl will readily Vadapt the structures and operating principlesdescribed to otherautomatic sample changers which, despitedifferences inappearance and details of construction, never' theless embody theessential teachings of the present nvention. 'It is accordingly to beunderstood that the scope of the monopoly conferred by the patent lawsshall be determined not from any details of construction herein shown ordescribed, but solely from the claims which are hereto appended.

What is claimed is:

1. In an automatic sample changer for radioactive samples, a housing, acarriage rotatably mounted von the housing and having at least threerecesses equally spaced and circularly disposed about the axis of thecarriage, dispensing and receiving magazines, anda radiation shieldhaving mouth portions, means for mounting the vmagazines and the shieldin relative positions corresponding to the relative positions of threeof the recesses, the mouth portions facing and being closely adjacent tothe rotational path of the recesses, a sample holder support in eachrecess having a depending portion extending through the carriage andadapted to be reciprocated to raise a samplevholder within the recessbeyond the surfaceV of the carriage and to lower a sampl holder in therecess to a'level substantially ilush with the carriage surface, a

stop member mounted on the housing in the portion of` the rotationalpath of said depending portions adjacent tok the'receiving magazine, amotor, a friction coupling be` tween' the motor and the carriage adaptedto `.rotate the carriage except when one of the'depending portionsen- Vgages the stop member, and a rotatable cam coupled to the motor andhaving a camming surface successively driving the depending portions ofthe sample holder supports in such three recesses to raise thesuccessive support members, whereby in each rotation of the cam a sampleholder within the shield is. lowered into a'recess in the carriage, asample holder within a recess in the' carriage is raised into thereceiving magazine, a sample holder in a recess is brought oppositel thereceiving magazine, a recess in the carriage is brought beneath thefdispensing magazine, a recess containing a sample holder is movedbeneath the shield, a recess receives a sample holder from thedispensing magazine and a sample holder in a recess is raised into theshield.

y2. .The sample changer of claim'l wherein the stop member extendsb'etweenrpositions adjacent tothe ktwo magazines, and comprises a platehaving opposite en ds adapted to engage said depending portions andhaving af flat surface between said ends adapted to support thedepending portions as they pass thereover, and there are provided meansfor reversing the motor, whereby each' sample holder support member ismaintained in'an ele-v vated position as it passes between magazines ineither direction, so that a, sample holder is deposited in one* magazinefrom each successive recess and another sample holder is received fromthe other magazine vin each successive recess, and the cycle may bereversed Vbyreversal of the motor.

' 3. In an automatic sample changer for radioactive samples, a housing,a rotatablecarriage journalled on the housing and ,having atleast threerecesses equally spaced and circularly disposed about the axis of thecarriage, dispensing and receiving magazines and a radiationshieldhaving mouth portions, means for mounting the magazines and thedshieldin a relative position corresponding tothe relative position of three ofthe recesses, the mouth portions facing and being closely adjacentgtothe rotational path of the recesses, a sample holder support member ineach recess adapted to be reciprocated to raise a sample holder withinthe recess beyond the surface of the carriage and to lower a sampleholder in the recessV to a level substantially flush with the carriagesurface, means to rotate the carriage so that each recess passes fromthe shieldl to one magazine, thence to the other magazine and then againto the shield, and means to ele-k vate each support member when it isopposite saidone magazine and to retract the support member when it isopposite said other magazine, so that successive sample holders areremoved from the mouth of said other maga7 zine, brought opposite themouth of the shield, and theny inserted and retained in the mouth vofthe rst magazine. y

4. In an automatic sample changer for radioactive samples, a rotatablecarriage plate having at leastvthree recesses in the upper surfacethereof, equally spaced from` of sample holders, and an open-bottomradiation shield,

means for supporting the magazines and the shield closely above thecarriage plate in the same relative spacing with respect to the axis ofrotation of the' carriage plate as three of said recesses, so that the`recesses successively pass beneath the magazines and the shield, asample holdersupport member in each recess, a motor, and cycling meanscoupled to the motor to lower the sample holder support member beneaththe shield to withdraw` a sample holder thereon from the shield,elevate` the support member in the recess beneath the receiving magaTzine to insert a sample holder` into the magazine, rotate provided meansresponsive to the emptying of the iirst magazine to reverse the cycle ofoperation and means responsive to the emptying of the second magazine torestore the original cycle of operation. f

6. The sample changer of claim 5 wherein there are rprovided means forinactivating the cycling means Vat the end of Leach of said originalcycles thereof for a period responsive to an actuating stimulus, andmeans disabling the inactivating means during the reverse cycles.

7. In an .automatic sample changer for radioactive samples, a rotatablecarriage plate having at least three re cesses in the upper surfacethereof, equally spaced from the'aXis of rotation and circumferentiallyspaced at equal angular intervals, open-bottom substantiallytubularven,y tical dispensing and receiving magazines adapted to re-yceivestacks of sample holders, and an open-bottom radiation shield,means for supporting the magazines and the shield closely above thecarriage plate in the same relative spacing with respect to the axis ofrotation of the carriage plate as three of said recesses, so that therecesses successively pass beneath the magazines and the shield, asample holder support member in the bottom of each recess having adepending portion extending downwardly through, and reciprocable in, theplate, so that a sample holder in the recess may be raised and loweredbyv raising and lowering of said depending portion, and means 15 forcyclically raising and lowering said support members and for rotatingsaid carriage plate to withdraw successive sample holders from thebottom of the dispensing magazine and insert them into Ithe shield andthereafter to Withdraw them from the shield and insert them into thereceiving magazine.

8. An automatic sample changer for radioactive samples comprising ahorizontally rotatable at-surfaced carriage having, equally spaced fromthe aXis of rotation thereof, and circumferentially spaced at equalangular intervals, at least three substantially identical upwardlyfacing recesses of a depth to receive a sample holder, verticalopen-bottom dispensing and receiving magazines each adapted to receive astack of sample holders, an open-bottom shield adapted to hold aradiation counter, means to support the open bottoms of the magazinesand the shield in circumferentially spaced relation at correspondingangular intervals above and closely adjacent to the rotational path ofthe recesses, elevating means in each recess to raise a sample holderabove the surface of the carriage, means to activate and deactivate theelevating means to raise and lower a sample holder in each recess whenthe recess is beneath the shield, and to raise a sample holder as therecess passes beneath the receiving magazine and means to rotate thecarriage to. successively position the recesses under the magazines andthe shield, whereby successive sample holders areV removed from a stackof sample holders in the dispensing magazine, inserted into and removedfrom the shield, and then loaded into the bottom of the receivingmagazine.

9. An automatic sample changer for radioactive samples comprising arotatable flat-surfaced carriage having equally spaced from the axis ofrotation thereof a plurality of circumferentially spaced substantiallyidentical recesses of a depth to receive a sample holder, dispensingandreceiving open-ended magazines each adapted to receive a stack of sampleholders, an open-ended shield adapted to hold a radiation counter, meansto support the open ends of the magazines and the shield incircumferentially spaced relation facing and .closely adjacent to therotational path of the recesses, elevating means in each recess to raisea 'sample holder above the surface of the carriage, means to activateand deactivate the elevating means to raise and lower a sample holder ineach recess when the recess is positioned at the open end of the shield,and to raise a sample holder as the recess passes the receivingmagazine, and means to rotate the carriage to successively positio-n therecesses at the ends of the magazines and the shield, whereby successivesample holders are removed from a stack of sample holders in thedispensing magazine, inserted into and removed from the shield, and thenloaded into the end of the receiving magazine.

l0. An automatic sample changer for radioactive samples comprising aflat-surfaced carriage having in the flat surface thereof a recess of adepth to receive a sample holder, dispensing and receiving verticalopen-ended magazines each adapted to hold a stack of sample holders, anopen-ended shield adapted to hold a radiation counter, means to supportthe open ends of the dispensing magazine, the shield and the receivingmagazine in spaced relation facing and closely adjacent to the flatcarriage,tmeans for moving the carriage in the plane of the flat surfaceto successively and repeatedly position the recess at the end of thedispensing magazine, the shield, and the receiving magazine, elevatingmeans to raise a sample holder in the recess above the surface of thecarriage, means to activate and deactivate the elevating means to raiseand lower a sample holder in the recess when the recess is positioned atthe open end of the shield, and to raise-a sample holder as the recesspasses the receiving magazine, whereby successive sample holdersareremoved from a stacl of sampleV holders in the dispensing magazine,inserted into and removed from the shield, and then loaded into andretained in the end of the receiving magazine.

11. An automatic sample changer for radioactive sarnples comprising ahorizontally rotatable dat-surfaced carriage having in the at surfacethereof an upwardly facing recess of a depth to receive a sample holder,an openbottom magazine elongated vertical adapted to receive a stack ofsample holders, an open-bottom shield adapted to hold aV radiationcounter, means to support the open bottomsV of the magazine and theshield in circumferentially spaced relation above and closely adjacentto the rotational path of the recess, means for rotating the carriage tosuccessively position the recess under the magazine and the shield,elevating means to raise a sample holder in the recess above the surfaceof the carriage, means coupled to the elevating means to activate anddeactivate the elevating means to raise and lower a sample holder in therecess when the recess is beneath the shield, and means to remove asample holder from the recess during its motion from the end of theshield to the end of the magazine, whereby successive sample holders areremoved from a stack of sample holders in the magazine, and theninserted into and thereafter removed from the shield.

l2. An automatic sample changer for radioactive samples comprising ashield adapted to receive a radiation counter, a magazine adapted toreceive a plurality of stacked sample holders, means for supporting saidshield and said magazine in mutually spaced relation, means adapted tobe connected to an activating stimulus for withdrawing successive sampleholders from the magazine and inserting them into the shield for a timeresponsive to the activating stimulus, means independent of theactuating stimulus for restacking the sample holders in the magazine intheir original order, and means for again Withd'rawing successive sampleholders from the magazine and inserting them into the shield for a timeresponsive to the actuating stimulus, whereby the samples are repeatedlycounted in successive order.

13. An automatic sample changer for radioactive samples comprising ashield adapted to receive a radiation counter, dispensing and receivingmagazines each adapted to receive a plurality of sample holders insuccessive order, means for supporting said shield and said magazines inmutually spaced relation, means adapted to be connected to an actuatingstimulus for withdrawing successive sample holders from the dispensingmagazine and inserting them into the shield and for withdrawing themfrom the shield after a time responsive to the actuating stimulus andinserting them into the receiving magazine, meansresponsive to theemptying of the dispensing magazine for withdrawing successive sampleholders from the receiving magazine and inserting them into thedispensing magazine to restore the sample holders to said dispensingmagazine in their original order, and means responsive to the emptyingof the receiving magazine to again initiate the original cycle ofoperation, whereby the samples are repeatedly counted in successiveorder.

14. The sample changer of claim 13 wherein the means to restore thesample holders to the dispensing magazine are independent ofsaid-actuating stimulus.

15. An automatic sample changer for radioactive samples comprising ashield adapted to contain a radiation counter, dispensing and receivingmagazines each adapted to receive a plurality of sample holders insuccessive order, means for supporting said shield and said magazines inmutually spaced relation, means adapted to be connected to an actuatingstimulus for withdrawing successive sample holders from the dispensingmagazine and inserting them into the shield and for withdrawing themfrom the shield after a time responsive to the actuating stimulus andinserting them into the receiving magazine, and,means independent of theactuating stimulus responsive to the emptying of the dispensing magazinefor withdrawingsuccessivesample holders from the receiving magazme andinserting them in the dispensing magazine to restore the sample holdersto the dispensing magazine in their original order.

1'6'l An automatic sample changer for radioactive samples comprising aradiation shield adapted to contain a radiation counter, dispensing andreceiving magazines each adapted to hold a plurality of sample holders,means for supporting said shield and said magazines in mutually spacedrelation, and means adapted to be connected to an actuating stimulus forwithdrawing successive sample holders'from the dispensing magazine andinserting them into the shield and for withdrawing them from the shieldafter a time responsive to the actuating stimulus and inserting theminto the receiving magazine, said withdrawing and inserting meanscomprising a sample-retaining member and means for moving thesample-retaining mem ber in a circular path, the supporting meanssupporting the shield and the magazines in spaced relation on thecircular path.

17. An automatic sample changer for radioactive samples comprising arotatable carriage having at least three sample-carriers circularlydisposed and spaced at equal angles about the axis of the carriage,substantially tubular dispensing and receiving magazines adapted toreceive a plurality of stacked samples in successive order and aradiation detector holder, vsaid magazines and detector holder having'mouth portions, means for mounting ythe magazines and the detectorholder in xed positions in relation to each other corresponding to therelative positions of three sample-carriers, the mouth portions facingrand being closely adjacent to the rotational path of thesample-carriers, and cycling means coupled to the carriage and to thesamp1e-carriers including means to rotate the carriage iu each cyclethrough an angle corresponding to the angle between adjacentsample-carriers, means operative in each cycle to insert a sample .fromthe dispensing magazine into thesample-carrier adjacent thereto, meansoperative in each cycle to insert a sample into the receiving magazinefrom the sample-carrier adjacent thereto, and switching means operativein each cycle and adapted to activate and inactivate a radiationdetector in the holder.

' 18. An automatic sample changer for radioactive samples comprising arotatablek carriage having a plurality of sample-carriers circularlydisposed about the axis of the carriage, substantially tubulardispensing and receiving magazines adapted to receive a plurality ofstacked samples in successive order and a radiation detector holder,said magazines and detector holder having mouth portions, means formounting the magazines and the detec- -rtor holder with their mouthportions facing and closely tive in each cycle to stop a sample-carrieropposite the.

mouth portion of the detector holder, means operative in each cycle toinsert a sample into the receiving magazine from a sample-carrieradjacent'thereto, and means for retaining samples in the magazinesduring rotation of the carriage.

19. An automatic sample changer -for radioactive samples comprising acarriage rotatable about a vertical axis and having at least threesample-carriers circularly disposed and spaced at equal angles about theaxis of the carriage, elongated vertical dispensing and receivingmagazines adapted to receive a plurality of samples in successive orderand a radiation detector holder having downwardly facing mouth portionsclosely adjacent to the rotational path of the sample-carriers inrelative positions corresponding to the relative positions of threesamplecarriers, motion-cycling means coupled to the carriage and to thesample-carriers including means to rotate the carriage in each cyclethrough an angle corresponding to the angle between adjacentsample-carriers, means operative in each cycle to lift a sample into thereceiving magazine from the sample-carrier adjacent thereto, andswitching means coupled to the motion-cycling means and operative ineach cycle and adapted to be coupled to a control circuit and to aradiation detector in the holder.

20. ln an automatic sample changer for radioactive samples comprising aradiation shield adapted to contain a radiation counter and means forinserting successive sample holders into said shield, the improvedconstruction wherein there are provided first and second elongatedsubstantially tubular magazines spaced from the radiation shield onopposite sides thereof, and adapted to receive a plurality of stackedsample holders in successive order and each having an open mouth, asample carrier, drive means coupled to the carrier for moving thecarrier along a closed path from the mouth of the first magazine pastthe shield and then past the mouth of the second magazine, and thenagain past the mouth of the first magazine, and actuating means coupledto the carrier for moving a sample in the carrier toward the mouth ofthe second magazine and way from the mouth of the rst magazine as thecarrier passes the mouths of the respective magazines, whereby thesample holders in one magazine may be successively received by thecarrier member, carried to the shield, and thereafter deposited in theother magazine.

21. In an automatic sample changer for radioactive samples comprising aradiation shield adapted to contain a radiation counter and means forinserting successive sample holders into said shield, the improvedconstruction wherein there are provided rst and second elongatedsubstantially tubular magazines spaced from the radiation shield onopposite sides thereof, and adapted to receive a plurality of stackedsample holders in successive order and each having a mouth portion, asample carrier, drive means coupled to the carrier for moving thecarrier along a closed path from the mouthrof thek rst magazine past theshield and thenpast themouth of the second magazine, and then again pastthe mouth of the tirst magazine, actuating meansV coupled `to thecarrier for moving a sample in the carrier toward the mouth of thesecond magazine and away from the mouthpfof the first magazine as thecarrier passes the mouths of the respective magazines, and means forreversing the action of the actuating means to move samples in thecarrier toward the mouth of the first magazine'and away from the mouthof the second magazine as the carrier passes the mouths of therespective magazines whereby the sample holders in one magazine maybe'successively received by the carrier, carried to the shield,deposited in the other magazine, and thereafter restacked in the firstmagazine in their original order.

References Cited in the le of this patent UNITED STATES PATENTS2,260,660 Darwin Oct. v28, 1941 2,350,273 Decker May 30, 1944 2,490,298Ghiorso Dec. 6, 1949 2,500,492 Henriques Mar. 14, 1950 2,570,660 GambleOct. 9, 1951 OTHER REFERENCES An automatic sample changer to be used formeasuring radioactive samples, Peacock et al., Review of ScientilcInstruments, vol. 17, No. 7, July 1946, pages kZ55-26,1.

